Contrasting Atomically Dispersed Metal Catalysts Supported on CeO x Nanoislands with Various Ligand Environments Including Chloride

Metals that are dispersed atomically on supports offer new and potentially valuable catalytic properties associated with their high atom efficiencies and opportunities for tuning their electronic properties by choice of the support and other ligands bonded to them. Herein, we report the synthesis of atomically dispersed Pt, Rh, and Ir anchored on CeO_x nanoislands on a high-area SiO₂ support. Synthesis from chloride-containing metal salts gave metal complexes chemisorbed on the supported nanoislands, with Pt being prototypical and having a structure approximated as Pt₁Cl₂O₄, as shown by X-ray absorption spectroscopy and calculations at the level of density functional theory (DFT). Calcination converted the adsorbed species into a structure represented as Pt₁O₆, embedded in the CeO_x lattice. The Pt₁Cl₂O₄ was observed to have a higher catalytic activity for CO oxidation than the chloride-free, embedded Pt₁O₆ species, and DFT results indicate the role of chloride in enhancing the catalytic activity of the isolated Pt, in contrast to its role as an inhibitor when Pt is present as nanoparticles. This work emphasizes the importance of the first coordination shell in controlling the catalytic properties of atomically dispersed noble metals.